Sleep apnea is a common sleeping disorder in which an obstruction of the throat or absence of respiratory response prevents air from entering the lungs. Halted breathing results in increased concentrations of CO2 in the blood stream, resulting in an unconscious, regulatory respiratory response. An escalating 10% of the general US population has clinically significant sleep apnea (Peppard 2013), where breathing stops repeatedly and interrupts sleep, leading to significant cardio-vascular morbidities, insulin resistance, neural injury, and accelerated mortality.
Current therapies for obstructive, central, and complex sleep apnea focus on ameliorating the physiological symptoms of sleep apnea. All currently available therapies attempt to open the soft tissue of the airway, most often through positive airway pressure, and thereby allow stable breathing without subconscious awakening from the rapid eye moment (REM) cycle. There are currently multiple approaches to increase positive airway pressure, including but not limited to Continuous Positive Airway Pressure (CPAP), Adaptive Servo-Ventilation (ASV), and Expiratory Positive Airway Pressure (EPAP).
Other approaches, while less common, include jaw displacement devices, surgery, and even novel pharmaceuticals. While targeting the direct cause of sleep apnea, closing of the throat and neurological “forgetfulness” to breathe, as the primary means to treat apneas, other therapies employ a holistic methodology to treat the associated medical disorders or medication side effects.
The standard therapy for sleep apnea is Continuous Positive Airway Pressure (CPAP). CPAP utilizes a machine that delivers positive air pressure through a facemask during sleep. The air pressure from the mask is greater than the surrounding air, and as a result, the upper airway passages are forced open for the movement of air. Contrary to popular belief, CPAP isn't a ventilator that breathes for the individual; instead it simply keeps the airway open so that the individuals can breathe for themselves. Keeping the airway open also prevents snoring, a major complaint of partners of individuals with sleep apnea. CPAP requires a blower, increased pressure and a tight fitting mask, rendering patients to reject it. CPAP entails the patient wearing a mask over their nose and mouth, through which an air blower blows air through the nasal passages. The pressure is constant and continuous, but can be adjusted during the night using a system which detects air flow limitations and adjusts its CPAP level accordingly.
CPAP has been shown to attenuate Obstructive Sleep Apnea (OSA), improve nocturnal oxygenation levels, and improve the ejection fraction. CPAP is effective when used correctly, but due to side effects, approximately 50% (Wohlgemuth 2014) of patients are intolerant or non-compliant, and even in “compliant” patients usage is usually limited to 4 to 5 hours/night, 5 days/week (Weaver and Grunstein 2008). At this time, CPAP is the most common and reliable treatment; it is considered the “gold standard” of sleep apnea therapy. Despite this, many patients find it uncomfortable and cumbersome, reflective of the noncompliance rate of 50% of patients (Wohlgemuth 2014). Most often patient dissatisfaction comes from the time and patience required in learning to adjust the CPAP mask, and the noisiness of the built-in humidifier. Moreover, as indicated CPAP usage has various side effects, some of which can include skin abrasions, bruising, chafing, nasal congestion or dryness, and abdominal cramping (Guilleminault and Abad 2004; Weaver and Grunstein 2008). Unfortunately, among other concerns, this minimal use of CPAP may not be sufficient to prevent cardiovascular sequelae (Dempsey 2010).
Adaptive Servo-Ventilation (ASV) systems, which are an alternative to CPAP, use advanced algorithms to monitor, predict, and control respiratory gas levels as well as maintain stable breathing patterns. There are three factors that contribute to these advanced algorithms, including: the patient's most recent, average respiratory rate; the instantaneous rate, direction, and change in patient's airflow; and a backup respiratory rate of 15 breaths per minute (meaning the machine will force air into the lungs if breaths aren't taken.) These features allow for minimal support during stable breathing, however, the moment hypopneas or apneas begin to occur, the machine increases air pressure to stabilize breathing. In essence, ASV systems ventilate the patient appropriately during periods of hypopneas or apneas, while reducing support during periods of hyperventilation and normal breathing. Unfortunately, ASV has recently been shown to have serious side effects in Congestive Heart Failure (CHF) patients with central apnea (Cowie 2015).
Expiratory Positive Airway Pressure (EPAP) is the most recent therapy to be approved by the FDA. This therapy utilizes small, single use “plugs” that are placed over each nostril before sleeping. The device permits air to move in freely, however, it increases air pressure in the patient dead space upon exhalation. The theory is that an increase in dead space airway pressure will keep the throat open, thus reducing apneic events. Kryger et al. (2011) describes that over a twelve-month period the number of events per hour was decreased from 15.7 to 4, meaning a decrease of nearly 71.3%. Furthermore, snoring was reduced by 74.4% and there was a compliance rate of 89.3% compared to a reported 46 to 83% of patients being noncompliant to the traditional CPAP therapy.
Despite the foregoing options, there are really very few effective treatments available for central and mixed apneas which often comprise a significant portion of apneas, even in OSA patients.
Accordingly, what is needed is a device that can be universally applied to treat all three forms of sleep apnea, eliminates economical inefficiencies, and avoids negative side effects, while still adequately preventing apneic events and maximizing patient comfort. Manipulating atrial pressure of carbon dioxide in arterial blood (PaCO2) should meet these criteria for the OSA patient. Accordingly, a device is needed which monitors and maintains CO2 concentration levels during sleep, accordingly adjusting levels to prevent apneas, while also being easy to use, minimally invasive, and universally marketable.